A power system is configured from numerous generators, loads, power transmission/distribution instruments and control devices. In a steady state, minor disturbances caused by load fluctuation and system switching are applied to the power system. When a malfunction such as a ground fault or short circuit of the system occurs, major disturbances are applied to the power system. Due to these disturbances, power oscillation having a plurality of oscillation mode components is generated.
When the oscillation mode components are small or attenuated quickly, the power system will be in a stable state because the system oscillation after the generation of disturbances is maintained within a sufficiently small range. Nevertheless, when the oscillation increases or is not attenuated and continues or is diffused, the generators may be shut down and a wide-area power failure may occur, and, consequently, stable operation may become impossible.
Pursuant to the expansion in the size of power systems, the tendency is the increase in power source capacity, installation at remote locations, and localization, as well as the consequential extension of power line length and multiple tidal currents. Because the influence from these changes will work toward the decrease in stability of the power system, there is concern of a chain-reaction influence to the major loss of power and wide-area power failure triggered by the power swing of generators during a system malfunction.
Thus, an online system stabilization control system for constantly monitoring the stability of the system and preventing/predicting the influence on a wide-area power failure is required.
In recent years, a PMU (Phasor Measurement Unit) for measuring the generating line voltage phase angle of the power system, substantially in real time, based on synchronous measurement using a GPS (Global Positioning System), is coming into wide use. It is now becoming possible to comprehend, in real time, the power oscillation phenomenon by using the online measured values of the system generating line voltage measured using the PMU.
Based on the foregoing background, proposed is a system stabilization control technology for a business operator operating a power system to monitor and stabilize the system condition. For example, PTL 1 discloses the following: “A power system stabilization device for stabilizing a phenomenon in which numerous generators of a power system becomes unstable due to a system malfunction of the power system to which a generator group consisting of a plurality of generators is connected by quickly blocking certain generators of a control target power plant connected to the power system, comprising: double-generator system model creation means for calculating, in cases where the power system is equivalently represented as a generator group in the control target power plant and a generator group in another primary power system during a steady state before the occurrence of the system malfunction, a generator constant and an initial state amount at a constant frequency of roughly several minutes; electric quantity detection means for detecting a voltage and a current and power of the control target power plant with the occurrence of the system malfunction as the activation condition; external reactance estimation means for inputting an electric quantity detected by the electric quantity detection means and computing an external reactance upon viewing the primary power system from a generating line of the control target power plant after elimination of the system malfunction; electrically controlled generator determining means for computing oscillation of two equivalent generators which equivalently represent an operation of the generator group in the control target power plant and the generator group in the other primary power system based on the generator constant and the initial state amount calculated by the double-generator system model creation means, the external reactance calculated by the external reactance estimation means and the electric quantity detected by the electric quantity detection means, and determining an electrically controlled generator required for stabilization, via an extended equivalent area method, based on the foregoing computation result and priority of electric control of the respective generators set in advance; and control means for paralleling off the generator selected by the electrically controlled generator determining means from the power system”.